These mites feed on the scales which are continually falling from our skin. They prefer a high humidity (80%) and temperature (25° C), and so are particularly common in beds. Surprisingly enough it is only quite recently that the presence of these mites has been observed. The discovery was made during an investigation of the causes of asthma. It had long been known that some patients react violently to house dust, but it was not clear what substances caused the attacks. It has now been shown that these mites are widespread wherever man lives, and that it is the dust containing them that causes the more acute attacks of asthma in sensitive patients. It is not only the mites themselves but also their cast skins and faeces which produce the symptoms, and as these are easily disturbed during dusting and bed making, people can inhale them in large numbers.
Apart from sprays it has been found that the best method to get rid of these mites is frequent and thorough vacuum cleaning of mattresses, etc. Fortunately, these mites are completely harmless to most people.